It has been conventional for a long time to include ball and socket components in the drive trains of unit injectors and valves of internal combustion engines. Such drive trains normally include a tubular shaft (push rod) into the ends of which pivot contact members constructed of a hardened material are plugged. However, the high compressive loads imposed between the ball and the socket components of push rods of such engine sub-system drive trains can result (within as little as 20,000 to 30,000 miles) in the surfaces of a ball and/or socket becoming worn to such an extent that undesirably large amounts of play occur which adversely impact upon the operation of the associated fuel injectors and valves. This occurs even with the hardened metallic surfaces of the ball and socket connection. Such wear is most common with either lower quality lubricating oils or with good quality lubricating oil in which anti-wear additives have become either depleted or inhibited in their normal functioning due to oil contamination during the course of its use in an engine. When such wear occurs, it is necessary to perform major servicing of the engine, and the associated vehicle must be taken out of use for a day or more.
Ball and socket joints for internal combustion engines, such as diesel engines, must exhibit a variety of desirable characteristics in order to satisfy the needs of modern day engines. For example, such ball and socket joints must exhibit outstanding wear characteristics, must have high strength properties, must be capable of withstanding thermal shock and corrosive environments, and, most importantly, must be able to retain these desirable characteristics at the high temperatures commonly encountered in internal combustion engine operations. Typically, such ball and socket joints are formed of metals, such as tool steel. However, despite their many desirable characteristics, metal joints exhibit significantly reduced strength characteristics at elevated temperatures.
It has been found that the use of ceramic components can produce a dramatic reduction in wear to such an extent that, even with a metal socket--ceramic ball combination, a life of as much as 500,000 miles can be expected before an unacceptable amount of wear occurs. This is an increase of as much as 20 times the life of prior art metal-to-metal ball and socket joints. Thus, a definite advantage can be achieved if the pivot insert plugs for push rods and the like are made of a wear resisting ceramic material.
The use of wear resisting ceramic material in connection with ball and socket joints is found in U.S. Pat. No. 4,184,213 to Heimke which discloses a ball and socket assembly wherein the bearing surfaces are coated with aluminum oxide ceramic and anchoring elements are composed of silicon nitride. Heimke's use of frictional components manufactured of ceramic is designed to avoid wear phenomena on the articulating surfaces of an articulatory endoprosthetic ball and socket joint. However, Heimke does not disclose a component designed to reduce the wear of highly loaded mechanical interfaces where contact stresses can be as high as 250,000 psi, such as in diesel type internal combustion engines. Nor does Heimke disclose the use of a joint lubricant, or of a ceramic which is sintered using sintering additives.
Japanese Printed Patent Document No. 57 13204(A) issued Jan. 23, 1982 to Kawamura discloses the use of ceramic in the joints formed at each end of a push rod. This Japanese patent document does not suggest the use of a ceramic to metal joint contact surface.
U.S. Pat. No. 4,719,187 to Bardhan et al. discloses the production of dense sintered ceramic bodies of silicon nitride densified by the addition of yttrium oxide, rare-earth metals, or aluminum oxides; the ceramic bodies exhibit excellent mechanical strength. However, Bardhan does not apply these ceramic bodies to ball and socket arrangements including joint lubrication.
U.S. Pat. No. 4,629,707 to Wolfe discloses a high strength, low weight, silicon nitride based article including the use of a lubricating material to form a self-lubricating material as a bearing replacement. However, Wolfe's ceramic compositions are relatively porous (10-37%) and would not likely have sufficient strength to be used in heavy-duty diesel engine ball-sockets.
Richon et al., U.S. Pat. No. 4,615,990, is directed to compositional details for obtaining highly dense, high strength silicon nitride.
None of these prior art references reduces the wear of highly loaded mechanical interfaces in diesel engines where contact stresses can be as high as 250,000 psi.